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Sept. 3, 1946.
K_ R, wENDT E1- A|_
2,406,978
SQUARE CODING WAVE GENERATOR FOR SECRET TELECOMMUNICATION SYSTEMS
Filed Aug. 12, 1944
3 Sheets-Sheet l
IN VEN T0115
JfurlE Ifadb
BY
Sept. 3, 1946. ‘
2,406,978
K. R. WENDT ETAL
SQUARE CODING WAVE GENERATOR FOR SECRET TELECOMMUNICATION SYSTEMS
Filed Aug. 12, 1944
3 Sheets-Sheet 2
By
68M
' Sept. 3, 1946.
K_ R, wENDT ET AL
2,406,978
SQUARE CODING WAVE GENERATOR FOR SECRET TELECOMMUNICATION SYSTEMS
Filed Aug. 12, 1944
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2,465,978
Patented Sept. 3, 1946
UNITED STATES ‘ PATENT OFFICE
2,406,978
SQUARE CODING WAVE GENERATOR FOR
SECRET TELECOMMUNICATION SYS
TEMS
I Earl R. Wendt, Hightstown, and Alda V. Bedford,
Princeton, N. J ., assignors to Radio Corporation
of America, a corporation of Delaware
"Application August 12;'19é4, Serial N0. 549,216
18 Claims. (Cl. 179——-1.5)
2
1
The present invention relates to secret tele
communication systems and more particularly to
an improved method of and means for generat
ing, utilizing and modifying square coding waves
in such systems.
The invention, by way of example, will be de
shaping circuit whereby the normally rounded
complex coding wave is changed to a correspond
ing square wave having amplitude symmetry with
scribed hereinafter as an improvement in a se
respect to its A.-C. axis. The resulting square
coding wave comprises an irregular combination
of successively positive and negative uniform am
plitude pulses of irregular duration, which are
tern wherein, for example, a speech signal com
prising a complex wave S is modi?ed by means
of a coding signal comprising a complex wave K
in a manner whereby the instantaneous ordinates 15
wave shape and polarity, di?ering, if at all, only
in average amplitude. Therefore, the reciprocal
circuit required in the system described in said
combined by multiplication with the speech sig
cret telecommunication system of the general
nal S for transmission of a coded wave.
type described in the copending U. S. application
Since the square coding wave merely involves
of Aida V. Bedford, Ser. No. 536,630 ?led May 20, 10
successive equal reversals of polarity, the recip
194A. Said copending application discloses a sys
rocal, or decoding, wave has the same general
of the resulting coded signals are the product SK ' ' copending application may be eliminated in the
instant system, since the same square wave shap
of the corresponding instantaneous ordinates of
the speech signal and the coding signal. The re
sulting unintelligible coded signals are transmit
ted by any conventional means to a receiver
wherein the coded signals are combined with de
lug circuit may provide both coding and decod—
ing waves for transmission and reception, respec
tively.
While the invention is described herein, by
way of example, as an improved method of and
coding signals, generated in the receiver, and
means for secret telecommunication, it should be
having instantaneous ordinates corresponding to
understood that the novel wave shaping circuit
the reciprocals of the corresponding instantane
ous ordinates of the coding signal component of 25 may have numerous other applications wherein
it is desirable to generate and utilize complex
the transmitted signal. The ?nal signals, there
fore, are derived from the product of the trans
mitted signal SK and the decoding signal l/K.‘
The coding and decoding signal generators, at
the transmitter and receiver, respectively, are dis
closed in said copending application as synchro
nized by means of special synchronizing pulse
signals each comprising a ?rst signal pulse im
mediately followed by a second signal pulse of
opposite polarity, which pulses may be superim 35
posed periodically upon the coded signals SK. At
the receiver, the reversal in polarity between the
two synchronizing pulses is employed to syn
chronize the decoding wave generator.
In said copending application, the coding wave 40
K is generated by periodically pulse-exciting a
multi-section delay network and selecting pre
determined delayed pulse components which are
' combined in predetermined polarity to provide
a rounded complex wave.
square waves having uniform amplitude sym
metry with respect to their Ac-C. axes. It should
be understood that, as utilized herein, the A.-C.
axis of a wave is the voltage or current level at
which the summation of all of the areas of rela
tively positive wave increments equals the sum
mation of all of the areas of relatively negative
wave increments.
Every complex wave has some
such A.-C. axis, but all of such waves do not have
uniform amplitude symmetry with respect to their
A.—C. axes.
An outstanding advantage of employing such
a symmetrical square coding wave in a secret tele
communication system is that the resulting coded
signal always is at its maximum possible trans
mission level, since the speech signal is multi
plied by uniiormly equal amplitude coding wave
increments. This results in maximum contimu‘
The delayed pulse 45 ous transmitter e?iciency and a correspondingly
component selection is varied continuously by
means of a complex switching mechanism to pro
vide a code wave which is non-repetitive for a
desired interval. Since the code wave is non
high signal-to-noise ratio. Also, the inherent
distortion provided by the reciprocal circuits of
prior systems is eliminated. The use of an A.-C.
axially symmetrical coding wave eliminates the
symmetrical, the reciprocal decoding wave l/K 60 necessity of removing and later rein-serting the
D.-C. wave component comprising an essential
must be derived from the synchronized code wave
part of axially dissymmetrical waves.
generator at the receiver by means of a novel
Among the objects of the invention are to pro
wave reciprocal circuit described in said applica
vide an improved method of and means for pro
tion.
The instant invention comprises a novel wave 55 ducing complex square waves having A.-C. axis
2,406,978
4
symmetry.
.
delay network by combining in either polarity
Another object is to provide an im
proved method of and means for secret telecon'n
differently delayed pulses derived from a plural
munication. An additional object is to provide
ity of such predetermined points along the delay
an improved method of and means for generat
ing coding and decoding waves in a secret tele
network.
Separate isolating resistors 15, ll, 19, 2 l, 23, 25,
communication system. A further object of the
invention is to provide an improved wave shaping
points along the delay network, and have their
circuit.
each have one terminal connected to diiierent
remaining terminals connected to separate mov
able contacts of a plurality of single-pole double
Another object is to provide a method _
of and means for converting complex dissymmet
rical waves to equal amplitude square waves hav
ing A.-C. axis symmetry.
10
A’ further object is to
provide a method of and means for generating
a complex electrical wave having a corresponding
reciprocal wave of substantially the same wave
throw switches 21, 29, 3|, 33, 35, 31.
The corre
sponding ?xed contacts of the several switches
are connected together to provide two lines 39,
4|, which are terminated through resistors 133,
45, respectively, to ground. The remaining ter
I
15 minal of the line 39 is connected through a cou
pling resistor 41 to the input circuit of a square
The invention will be described in greater detail
by reference to the accompanying drawings of
wave shaping circuit49, described in detail here
inafter by reference to Figures 5 and 6, which
which Figure 1 is a schematic block circuit dia
provides equal amplitude positive and negative
gram of a complete secret telecommunication sys
tem employing the invention, Figure 2 is a series 20 wave increments having symmetry with respect
to their A.-C. axis. The remaining terminal of
of graphs illustrating the circuit operation of the
the‘ second line 4| is connected through a polar
transmitting portion of the system shown in Fig
ity-reversing ampli?er SI and a second coupling
ure 1, Figure 3 is a series of graphs illustrating
resistor 53 to said input circuit of the square
the operation of the receiver portion of the cire
wave shaping circuit 49.
'
‘
cuit illustrated in Figure 1, Figure 4 is a schematic
circuit diagram of the wave multiplier forming a
Thus, each of the 100 pulses per second, derived
from the multivibrator l and applied to the in
portion of the circuit of Figure 1, Figure 5 is a
put of the delay network 2, provides a plurality
schematic circuit diagram of a square code wave
of equalramplitude pulses of either polarity oc
shaping circuit comprising the basic element of the
curring at predetermined intervals during each
invention, and forming a portion of the system
one-hundredth second period, as determined by
shown in Figure 1 and Figure 6 is a series of
the points of connection to the delay network
graphs explaining the operation of said wave
and the arrangement of the switches 21, 29, 3|,
shaping circuit. Similar reference characters
33, 35, 31. Therefore, a very complex sym
are applied to similar elements throughout the
metrical square coding wave may be applied from
drawings.
the output circuit of the square wave shaping
Coding wave generator
circuit 49 to one input circuit of a wave multi
Referring to Figure 1, the coding wave ‘gener
plier, to be described hereinafter by reference to
ator employed for both transmitting and receiv
Figure 4 of the drawings, merely by selecting
ing coded speech signals comprises a conven
* the desired arrangement of the pulse selecting
tional free-running multivibrator circuit l which
switches. It should be understood that the total
generates pulses at a rate, for example, of one
delay provided by the pulse delay network pref
hundred pulses per second. A typical multi
erably should be at least slightly less than the
vibrator of this type, the frequency of which may
pulse period of the multivibrator l in order that
be controlled by recurrent applied control pulses, “‘ only one pulse may be traveling along the dela
network at any predetermined instant.
‘
is described in U. S. Patent 2,266,526, granted to
E. L. C. White on December 16, 1941. It should be
In the typical secret telecommunication sys
understood that pulses of either polarity may be
tem, described in said copending application
applied in any known manner to key the multi
. identi?ed heretofore, the coding signal generator
vibrator, and that, similarly, output pulses, of
includes a delay network having 80 sections and
‘either polarity may be derived therefrom. The
a plurality of sequential switches which may be
generated pulses are applied to the input of a
preset to any desired code and selectively actu
conventional delay network 2 comprising a plu
ated by a clock or motor mechanism to change
rality of series inductors 3, 5, ‘l, 9, II and a plu
the code continuously, or at predetermined de
rality of shunt capacitors 4, 6, 8, I0, I2, I4. The
sired intervals. Identical coding signal gener
remote terminals of the resultant pulse delay
ators are'employed at both the transmitter and
form.
network 2 are terminated by a resistor 13 match
ing the surge impedance of the network. It
should be understood that the delay network 2
may include a relatively large number of ?lter
sections as indicated by the dash lines inter
connecting the ?lter sections 1, 8 and 9, m, and
that equalizers and booster ampli?ers may be
inserted in the delay network at desired points
to maintain pulse amplitude relations at optimum.
values.
Pulses applied by the multivibrator I to the
input of the delay network 2 provide similar
pulses at the junction of each of the succeed- ,
ing series inductors 3, 5, 1, 9, I I, wherein each
succeeding pulse is delayed a predetermined
amount with respect to pulses occurring at pre
ceding terminals of the network. A complex, but
generally rounded, coding wave thus may be 0b- 1.
tained in response to each pulse applied to the
receiver in such a secret telecommunication sys
tem. By means of . simple “transmit-receive”
switches the square wave coding signal either is
"' combined with the speech signal for transmit
ting a coded wave, or the same wave shape re
ciprocal values of the coding signal are derived
from the same square wave shaping circuit 49
responsive to the coding signal generator and
' are combined with the received coded signal to
decode said received signal.
Much of the de
coding apparatus including the generator and
wave shaping circuit for the code signal is iden
tical to the coding apparatus. Hence, by means
of the simple “transmit-receive” switches, the
various elements of the apparatus may be em
ployed at different times, and in some instances
with somewhat different adjustment, for dual
purposes in a single unit for either transmitting
or receiving the coded signals.
2,406,978
trated in Figure 2, which is applied to the input
of the delay network 2 to initiate a succeeding
pulse which will be progressively delayed along
Coding transmitter
Referring to Figures 1 and 2, the system may
be employed as a coding transmitter'by switch
ing the movable contacts of each of the single
the delay network. Since the ?rst multivibrator
I is keyed by the pulse from the third multivibra
pole, double-throw “transmit-receive” switches
tor “(1 immediately preceding the time for the
included therein to engage the ?xed contacts
generation of a normal pulse by said ?rst multi
T1, T2, T3, T4, and T5, corresponding to the
vibrator, it will be seen that the coding wave gen
“transmit” condition. Signals derived, for exam
orator will be self-running, and will be main
ple, from a microphone 55, which may be fed
tained at a substantially constant frequency,
10
through a speech ampli?er, not shown, are ap
since the pulse rate therethrough will be substan
plied through a ?rst “transmit-receive” switch
tially dependent upon the time delay of the suc
51 to one input circuit of a wave multiplier 59,
cessive pulses applied to the delay network 2.
which will be described in detail hereinafter by
If for any reason the ?rst multivibrator l is
reference to Figure 4 of the drawings. Coding
15 not properly keyed by the third multivibrator 11,
U1
signals, from the coding signal generator and
the ?rst multivibrator will merely generate a
pulse 6’ which will be applied to the delay net
work 2 at a slightly later interval. The slightly
multiplier 59, whereby coded signals SK having
delayed pulse upon reaching the seventy-ninth
instantaneous ordinates corresponding to the
tap of the delay network therefore will key the
20
products of the corresponding instantaneous or
second and third multivibrators in the manner
dinates of the speech signal S and the symmetri
described heretofore and provide a new set of syn
cal square wave coding signal K are applied
chronizing pulses which will actuate the ?rst
through a second “transmit-receive” switch 6|
multivibrator l in synchronism thereafter.
to one input circuit of a ?rst signal mixer circuit
The coded signals SK combined with the syn
63, which may comprise any conventional net! 25 chronizing pulses c and d are applied to a second
work wherein applied signals are combined alge
limiter 19 whereby the high amplitude portions
wave shaping circuit described heretofore, are
applied‘ to a second input circuit of the wave
braically.
Transmitter synchronizing pulse generator
Regularly recurrent pulses indicated by the
graph a of Figure ‘2 are derived, for example,
from the seventy-ninth tap on the delay network
2 and are applied to a conventional thermionic
tube amplitude limiter circuit 61, which clips the
I of the synchronizing signal are clipped to a
maximum level II indicated by the dash lines in
graph. f of Figure 2. The thus limited combined
coded and synchronizing signals are applied as
a communication signal to a conventional radio
transmitter 8| which includes a transmitting an
tenna 83.
Coded signal receiver
wave a at the level w to derive individual limited 35
pulses represented by graph b‘ of Figure 2. The
‘limited pulses b are applied through a third
“transmit-receive” switch 69 to key a second
multivibrator H to derive a negative substan
tially squarewwave pulse illustrated by graph 0
of Figure 2. The negative square wave pulse 0
is applied through a fourth “transmit-receive”
switch i3 to a second input circuit of the ?rst
In order to convert the circuit thus described
to operate as a coded signal receiver, the mov
able contacts of each of the “transmit-receive”
switches 51, SI, 69, 13 and 15 are switched to the
corresponding ?xed contacts D1, D2, D3, D4, D5,
corresponding to the “receive” condition. Be
cause of the in?delity of the radio transmitter
and receiver, the combined coded signal and syn
signal mixer circuit 63, and also is applied 45 chronizing signals transmitted from the trans
through a ?fth “transmit-receive” switch ‘I5 to
mitter Bi and received by a conventional radio
key a third multivibrator 1'! which generates a
positive square wave pulse indicated by the graph
d of Figure 2. It will be understood that the
positive square wave pulse (1 will be initiated at
the termination of the negative square wave pulse
0 in a manner well known in the multivibrator
art, The positive square wave pulse 11 is applied
to a third input circuit of the signal mixer cir
cuit 53 whereby the coded signal SK, the nega
receiver 85 are “smeared” and phase-shifted
somewhat to resemble, the solid portion m of the
graph f of Figure 2. These received signals are
applied to a conventional wave differentiating
network Bl, which may be of any type well known
in the art.
For example, a wave may be differ
entiated by applying it to a network comprising
a small series capacitor and a shunt resistor. The
transmitted signal m of Figure 2 after being dif
tive square wave pulse 0 and the positive square 55 ferentiated at the receiver resembles the graph g
Wave pulse (2 are combined to provide a communi
cation signal including the coded wave SK and
of Figure 3 wherein a relatively large pulse P
the synchronizing signal comprising a negative
square wave pulse immediately followed by a pos
polarity between the received synchronizing
negative and positive pulses and wherein low fre
itive square wave pulse.
It should be understood that, if desired, the
synchronizing signal may comprise a positive
pulse followed by a negative pulse since multi
vibrators may be keyed by, and can provide, pulses
of either polarity, providing proper connections
thereto are provided in a manner known in the
art. The combined coded signal and synchro
nizing signal derived from the mixer 63 will have
a waveform, for example, of the type illustrated
in graph 1‘ of Figure 2, including the pulses I, I,
shown ‘in dash lines.
A pulse derived from the third multivibrator 11
also is applied to key the ?rst multivibrator l
to generate a positive square wave pulse e, illus
occurs at an instant corresponding to the reversal
quency components are substantially removed
from the pulse P. It should be understood that
instead of differentiating the received signal, it
may be treated in any other known manner to
derive a pulse in response to the reversal in polar
ity of the negative and positive synchronizing
pulses.
The receiver ?rst multivibrator I being free
running, as described heretofore, the delay net
work 2 will provide recurrent pulses at its sev
enty-eighth tap which will be limited by means
of a third limiter 89 to provide limited pulses
represented by the graph h of Figure 3. The
thus limited pulses h are applied to key a fourth
multivibrator 9| which generates a relatively long
2,406,978.
7
8.
blanking ‘pulse illustrated in graph iof Figure-3.‘
The long blanking pulse 1' is applied to a blanking
radio circuits interconnecting the transmitter and
receiver units, it is possible that the effective
circuit 93 which blanks out portions of the re
time of occurrence of the received synchronizing
ceived signal, as Will be explained in greater de
pulses will vary in different receivers with re
tail hereinafter.
Receiver synchronizing circuits
spect to the received coded speech. To correct
for such variations, the circuit constants of the
third multivibrator 11 may, in any known man
Similarly, each of the recurrent pulses derived
ner, be altered in the receiving condition so that
from theeightieth tap of the delay network 2
the width of the pulse it may be varied to provide
are applied to a fourth limiter 95 which clips the 10 keying of the first multivibrator l at the precise
upper portion of the applied pulse as explained
desired instant. The manner of varying the cir
heretofore with respect to pulse 17, to provide a
cuit constants of multivibrators to provide pulses
short pulse illustrated by graph 7' of ‘Figure 3.
or desired polarity and duration in response to
7its limited pulse 7' is applied through the third
predetermined applied triggering pulses is Well
“transmit-receive” switch 69 to key the second 15 known in the art.
multivibrator ‘II to provide a relatively long posi
Signal decoding system
tive square wave pulse It. It will be noted that
the positive pulse is is of relatively longer dura
The received signals derived from the radio re
tion than the negative pulse 0 previously de
ceiver 85 are applied to the input of the blanking
scribed as generated by the second multivibrator
_ circuit 93 which interrupts the received coded
‘H when said multivibrator is employed in the
signals during the occurrences of the recurrent
transmitting circuit.
The different pulse polar
blanking pulses 2', whereby the transmitted posi»
ity and duration may be accomplished in any well
tiveand negative synchronizing pulses may be
known manner by changes provided in the multi
removed from the received coded signal. This
vibrator circuit constants and the connections 251 condition obtains when the coding signal gen~
erator of the receiver is in synchronism with the
thereto, when the multivibrator is switched from
the “transmitting” to the “receiving” condition.
transmitter coding" signal generator, since the
fourth multivibrator 9| is responsive to pulses de
The positive square wave pulse is derived from
rived from the seventy-eighth tap on the delay
tlie'second multivibrator ‘H is applied through
network 2. Blanking circuits are well known in
the fourth “transmit-receive” switch 13 to a sec
ond'mixer circuit 9'5, to which also is applied the 30' the art. They may comprise, for example, a
push-pull ampli?er for the signal, arranged so
diiierentiated wave In derived from the differen
that the blanking pulses i are superimposed on
tiating circuit 87. The thus'mixed signals illus
the grid-cathode circuits so that both tubes are ,7
trated by graph Z of Figure 3 include a pulse peak
1’ which corresponds in time to the occurrence 35 simultaneously driven to cut-off during the blank
ing period. The thus blanked received signals
of the large positive pulse P of the differentiated
comprise the transmitted signal components SK .
received wave 0. As explained heretofore, the
which are applied through the ?rst “transmit
pulse P corresponds .to the reversal in polarity of
receive” switch 5? to one of the input circuits of
the received synchronizing negative and positive
the wave multiplier 59.
pulses. The wave Z derived from the second
Similarly, the signals generated by the receiver
mixer circuit 91 is applied to a ?fth limiter 99
coding generator are applied to the input circuit
which clips the mixed signal at a level 1/ to pro
of the square wave shaping circuit 49, which
vide in its output circuit a short somewhat tri
angular pulse, illustrated by graph in of Figure 3.
will be described in detail hereinafter by refer
The triangular pulse in is applied through the
ence to Figure 5 of the drawings. The square
wave output of circuit 49 has the same positive
?fth “transmit-receive” switch 15 to key the third
and negative amplitudes (measured from the
multivibrator ‘H to provide a positive pulse repre
sented by graph n of Figure 3 which is applied to
A.-C. axis). Hence this wave is identical in shape
to its own reciprocal wave, and the same wave may
key the ?rst multivibrator I as described hereto
fore with respect to the pulse d in the transmit 50 serve as K in the sending unit and as l/K in the
receiving unit. Thus-the square wave output of
ting network. It should be understood that, if
desired for extremely precise synchronism, the
circuit 49 is applied (as the reciprocal wave l/K).
to a second input circuit of the multiplier 59.
pulse in may be changed from triangular to
Since the wave multiplier 59 provides output sig
square wave shape by clipping at a low level and
then by amplifying the clipped lower portion of
nals which have instantaneous ordinates corre
sponding to the product of the instantaneous
the pulse in a‘manner known in the art. The
pulse n therefore causes the ?rst multivibrator l
ordinates of the waves l/K and SK applied there
to, the output signals S’ applied through the sec"
to generate a positive pulse 0 which is applied to
ond “transmit-receive” switch iii to a reproducer
the delay network 2 in the same manner as de
scribed heretofore with respect to the positive 60 I03 will be substantiallyocharacteristic of the
original speech modulation signals S. The sig
pulse e of the transmitting network.
As explained heretofore with respect to the
nalsapplied to the reproducer I03 have been in
operation of the multivibrator circuits in ‘the
dicated as S’ since some distortion is inherent in
"transmitting” condition, if the circuit falls out
the_various circuits described and especially in
of synchronism, the various multivibrators will 65 many radio transmission circuits. It should be
provide pulses at somewhat increased time inter
understood that the signals S’ derived from the
vals ‘ until such time as a synchronizing pulse
second “transmit-receive?’ switch 6| may be ap
occurs at a proper instant to pull all of the multi
plied to actuate any other desired type of utiliza
vibrators back into synchronism. Since pulses are
tion apparatus, not shown.
derived from the delay network 2 at intervals of 70
Signal multiplier
the order of .01 second, it is apparent that the
Figure 4 shows a typical wave multiplier cir
various circuits will fall into synchronism in ‘a
cult forming a portion of both the coding wave
relatively short time which seldom will exceed one
transmitter'and receiver circuits described here
full second. '
'
Due to phase distortion in the transmission or 75 tofore with reference to Figure 1 of the drawings.
2,406,978
9 .
This multiplier circuit is described and claimed
in the copending U. S. application of Alda V.
Bedford, Serial No. 511,967 ?led January 12, 1944
and assigned to the same assignee as the instant
l0
ignated in the circuit diagram. As shown, the
network also includes shunt resistors i3I and I33
leading respectively from points (S—K) and
(—S+K) to ground, and shunt resistors I35 and
application. The circuitrutilizes the property of 5 I31 leading respectively from points (S+K) and
well known electrical devices which provide an
(~S—K) ‘to the positive terminal of the source
instantaneous output current or voltage which is
of bias voltage which is applied through a volt
proportional to the square of the instantaneous
age-reducing resistor I33. An 8QGO-ohm resist~
input voltage over a reasonable voltage range in
ance has been found satisfactory for the shunt
a single polarity. Such circuits or devices will be 10 resistors I3i, I33, I35, and I31 while 100,000-ohm
referred to as “squaring circuits,” and will be
resistance has been taken as the value of the se
designated as “Q” where referred to hereinafter.
In ‘the preferred form of the multiplying cir-
ries bridge ‘resistors H5, H1, H9, I2I, I23, I25,
I21, and I29.
cuit, the waves S and K, (or SK and l/K),
The sum voltages at the four points of the
to be multiplied, are added together with four 15 network are applied with the bias voltage A and
different polarity combinations and “squared” in
—A to four varistors V1, V2, V3, and V4 respec
foundifferent signal channels. Then the four
tively, all of which control the current through
“squared” signals are added together with suitthe common load resistor I 4] to provide there
able polarities to obtain the product SK, (or S),
across the product output voltage SK. The out
in the output circuit of the multiplier network, 20 put across the load resistor Ill is proportional to
as will be illustrated by the following equations
the sum of all the voltages which would have
for obtaining the product of S and K:
been generated if each varistor had supplied our
(1)
=s1+KY+A¢+2sK+2KA+2As
It will be understood ithat the term A in the
above equations is the D.-C. bias added to the
A.-C. waves to cause all of the signal amplitude
variations to have the same polarity with respect
to the squaring devices.
The squaring circuit illustrated employs a plu
rality of small copper oxide recti?ers known com
mercially as “varistors”. Because of the particu
lar variable resistance characteristics of the
“varistor,” the current therethrough is substan
tially proportional to the square of the applied
voltage over a reasonable range of applied volt
age of a single polarity. The multiplier network
53 is shown as including a ?rst triode thermionic
tube III having its grid electrode connected to
the ouput circuit of the square wave shaping cir
rent to a separate resistor, as indicated by the
foregoing squaring equations. It is .to be noted
that the varistors V2 and V4 are connected with
opposite polarities from the varistors V1 and V3,
so that the D.-C. bias voltage must be diiferent.
By reference respectively to the third and fourth
35 equations it will be seen that the values
and (S--K—A) are each preceded by another
minus sign and included in brackets before squar
40 ing to indicate properly mathematically the eifect
of the reversed connection on these two varistors.
These five equations show that, ideally, only the
desired voltage SK is produced across the output
resistor Ml.
For compensating for small dissimilarities in
cuit A9, whereby signals characteristic of either 45
the varistors and other circuit elements, it has
the coding wave K, or the reciprocal thereof 1/ K,
been found desirable to provide variable resis
may be applied to the tube grid-cathode circuit.
tors I43 and I45 connected as voltage dividers in
A second thermionic tube II3 has its grid elec
the anode circuits of the tubes III and H3, re
trode connected to the movable contact of the
spectively, for adjusting the relative amplitudes
?rst “transmit-receive” switch 51, whereby either
of -S and --K.
‘the speech signals S or the blanked, received sig
While in the foregoing the term “multiplying
nals SK may be applied to the tube grid-cathode
circuit” has been used to define the circuit, it will
circuit. The operation of the circuit will be ex
be seen that the circuit acts like a modulator
plained hereinafter with the switch 51 in the
“transmitting” position whereby the signals K 55 which is completely balanced in the sense that
only the side band frequencies are produced, while
and S, respectively, are applied, respectively, to
the input frequencies and the harmonics thereof
the grid-cathode circuits of the tubes III and
are suppressed.
H3. Push-pull output signals are derived from
The output signals SK derived from across the
each of the tubes by means of connections to the
corresponding tube anode and cathode circuits as 60 output resistor MI are applied to the movable
indicated in the drawings.
In order that the desired sum voltages be ob
tained, the signals S and K are applied to a
contact of the second “transmit-receive” switch
6|, whereby they may be selectively applied to
either the reproducer I83 or to the ?rst mixer
63, depending upon the desired operation in the
closed network of serially-connected resistors in
the following manner: Signals S and K, respec 65 circuit of Figure 1.
tively, traverse resistors H5 and ill to provide
Symmetrical square wave shaping circuit
a signal proportional to (S-l-K) at the point
Referring to Figures 5 and 6, the symmetrical.
(S+K) ; the signals S and -K respectively ,trav
square wave shaping circuit 49 includes an input
erse resistors H9 and I2I to provide a signal
(S-K); the signals -S and -K respectively 70 terminal I5! connected to the output of the code
wave generator coupling resistors 41, 53, and an
traverse resistors I23 and I25 to provide a signal
input terminal I53 which is grounded. The un
(—S-K); and the signals —S and K traverse
grounded input terminal I5I is connected
respectively resistors I21 and I23 to provide a
through a coupling capacitor I55 and a series
signal (—S+K). Thus, at each of the four junc
tion points, a sum of voltage is obtained as des 75 resistor I51 to the anode and cathode, respec
2,406,978
11
12
tively, of a pair of oppositely-connected diode
limiters I59 and IBI. The cathode of the diode
be readily constructed which provides symmetry‘
I 59 and the anode of the diode I'GI are connected
to suitable spaced points on a voltage divider
I83, I65, I51, I69 which is connected across a
source of bias voltage not shown: The junction
cuit operation.
within the order of two percent with stable cir
Thus the square coding wave K shown in graph
u of Figure 6 comprises equal amplitude positive
and negative square wave increments with re
of the voltage dividing resistors I65, I61 is con
nected through a capacitor Ill to ground. The
spect to its A.-C. axis which is at ground poten
tial.
A symmetrical square coding wave, as shown
output of the diode limiters I59, MI is applied
through a grid capacitor I73 to the control elec 10 in graph u of Figure 6, is to be desired over an
trode of a triode ampli?er I15. The cathode of
unsymmetrical square coding wave of the type
the triode ampli?er I15 is grounded through a
shown in graph 1), since the symmetrical square
cathode resistor ITI which provides normal bias
wave has a reciprocal wave which is the same
therefor. The grid of the triode ampli?er H5
shape as the original wave. As shown in graph
is connected through a grid resistor I19 to 15 '0 the A.-C. axis ofan unsymmetrical square wave
ground. Therefore, they 'code wave shown in
does not correspond with the zero axis Z1 of the
graph t of Figure 6, will be limited by the diodes
reciprocal of such a wave. Hence, if an unsym
I59, I5I at the levels q and'r determined by the
metrical coding wave were employed, a D.—C‘.
?xed biasvoltages applied to the diodes, where
component equivalent to the difference between
by the code wave will bc?changed to a substan 20 the A.-C. aXis and Z1 axis, illustrated, would be
tially square waveform, the positive and nega
necessary to provide proper decoding of the re
tive wave increments of which are not necessarily
ceived wave SK. Since the D.-C. component
symmetrical with respect to its A.-C. axis.
would vary continuously as the characteristics of
A source of anode potential, not shown, is con- ,
the coding wave changed, extremely elaborate
nected through an anode resistor IBI to the an 25 circuits would be necessary for such D.-C. inser
ode of the triode ampli?er I15. The anode of"... L . tion; If the proper D.-C. component were, not
the triode ampli?er I15 also is connected through
an output coupling capacitor I83 to one of the
circuit output terminals I85. The remaining
output terminal I8‘! is grounded.
30
A pair of oppositely-connected diode peak de
tectors I89 and I9I are connected across the out
put terminals through capacitors I93, I95, respec
tively. A voltage divider comprising the serially
connected resistors I97, I99 is connected be
tween the ungrounded terminals of the capaci
tors I93, I95 to provide a junction point 2llI hav¢
ing a control voltage equivalent to the difference
of the magnitudes of the positive and negative
Thus the invention described comprises a novel ,
wave shaping circuit wherein a complex electri
cal wave may be changed to a corresponding wave
45
to ground.
having equal magnitude positive and negative
square wave increments with respect to its A.-C.
axis. The novel circuit has been illustrated here
in as an element of a secret telecommunication
I95, being equal and relatively high, the voltage
at the point 2!“ will vary relatively slowly be
tween positive and negative values as the lim
ited code wave varies in symmetry with respect
coded SK signal components which would distort
the decoded signal component S’.
It should be understood that the symmetrical
square wave shaping circuit thus described may
be employed for many purposes other than that
described herein with respect to secret telecom
munication systems, since the network provides
a convenient method of and means for convert
ing any complex wave to a corresponding square
wave having equal magnitude positive and nega
tive wave increments with respect to its A.-C.
axis.
peaks of the square wave at the output termi
nals, with respect to ground, since one output ter
minal I81 is grounded and the remaining output
terminal I85 is connected to ground through a
loading resistor 293.
The time constant of the networks comprising
the resistor I91 and capacitor I93, and the net
work comprising the resistor I99 and capacitor
present in the decoding wave generator, the de
coded output would contain non-intelligible
system employing a communication signal which
is distorted by multiplication with such a sym
so
metrical square coding wave, and which is de~
coded by means of a similar synchronized sym~
_
metrical square coding wave.
The control potential derived from the point
'7
' We claim as our invention:
29! is applied to the control electrode of a triode
control tube 295, the cathode of which is ground;
ed. The positive terminal of the anode poten
1. In a secret telecommunication system for a
' communication signal, means for producing a
tial source is connected through a second anode
tude positive and negative wave increments with
respect to its A.-C. axis, and'means for, com
complex square coding wave having equal ampli
resistor 29'! to the anode of the control tube 295'.
The anode of the triode control‘ tube 295 also is
bining said coding wave with said communication
connected through a high impedance resistor 209
signal to provide a coded transmission signal.
2. In a system of the type described in claim
1, means for producing a second substantially
identical square wave, and means for combining
said second'wave with said transmission signal
to the common’terminals of the input coupling -
capacitor I55 and input coupling resistor I51,’
whereby a variable bias voltage of the proper
polarity is applied to the diode limiters I59, |6I
whenever the square coding wave across the out
put terminals I85, I81 tends to be dissymmetrical
with respect to ground. The thus applied bias
to decode said signals.
voltage thereby changes the normal limiting lev
els of the input signal'to provide uniform ampli
tude positive and negative square wave pulses
with respect to the wave A.'-C. axis. In common
with other automatic control circuits the control
provided by the control tube 205 approaches ideal
70
l
‘
‘
'
'3. In a system of the type described in claim
1, means‘ for producing a second substantially
identical square wave, means for synchronizing
said substantially identical square wave produc
ing means with said coding wave, and means for
combining said second wave with said transmis
sion signal ‘to decode said signals.
’
4. The method of communication which com;
conditions if the control tube circuit has rela
prises producing a communication signal and ya
tively high gain. An experimental circuit may 75 square wave distorting signal 'symmetricalv'vith
‘2,406,978
'13
respect to its A.-C. axis, multiplying the values
of said signals as measured from their alter
nating-current axes by each other to obtain their
product, transmitting said product to the point
of reception and there multiplying said product
by a similar symmetrical square wave signal hav
ing substantially the same waveform as said dis
torting signal, said last multiplication also being
14
1G.‘ The invention according to claim 6 ail-here
in means is provided for maintaining said code
signal producing means and said decoding signal
producing means in synchronism.
11. A transmitter-receiver unit for the trans
mission and reception of a communication signal,
said unit comprising means for producing a
square wave distorting signal having A.—C. axial
symmetry, multiplier means for multiplying said
a multiplication of the signal values as measured
from their alternating-current aXes.
10 signals by each other when applied thereto,
5. The method of communication which com
switching means for applying said communica
prises producing a communication signal and a
ticn signal and vsaid distorting signal to said mul
square wave distorting signal having A.-C'. axial
tiplier means to obtain their product, means com
symmetry, each of which comprises frequency
inch with said distorting signal producing means
components lying within a common frequency 15 for producing a similar square wave decoding sig
band, multiplying said signals by each other to
nal having substantially the same waveform as
obtain their product, transmitting'said product
said distorting signal, and switching means for
signal to the point of reception and there mul
supplying a received product signal and said de
tiplying said product signal by a similar sym
coding signal to said multiplier means to obtain
metrical square wave signal that is substantially 20 and decode said received communication signal.
the reciprocal of said distorting signal.
'
6. A system for transmitting a communication
signal from a transmission point to a reception
12. In combination with a secret telecommuni
cation system of the type wherein a communica
tion signal is combined with a modi?ed coding
signal by wave multiplication of the signal values
point which comprises means at the transmission
point for producing a square Wave distorting 25 with respect to the A.-C. axes of said signals, a
signal having A.-C. axial symmetry, means for
wave modifying circuit for said coding signal
multiplying said communication signal by said
comprising means for limiting positive and nega
distorting signal to obtain their product, and
tive increments of said coding signal, means for
means located at the point of reception for multi
amplifying said limited signal increments, means
plying said product by a similar symmetrical 30 for peak detecting said ampli?ed signal incre
square wave signal having substantially the same
ments, means responsive to said detecting means
waveform as said distorting signal, both of said
for deriving control potentials characteristic of
multiplication being a multiplication of the sig
the algebraic sum of the amplitudes of said de
nal values as measured from the alternating
tected signals with respect to its A.-C_ axis, and
current axes of the signals.
means for applying said control potential as a
7. In a system for secret transmission of a
variable bias potential on said limiting means to
communication signal, a communication unit that
provide from said phase inverting means a modi
includes means for producing a square wave dis
torting signal having A.-C. axial symmetry, and
means for multiplying the instantaneous ampli
tude of said communication signal as measured
fied coding wave having equal amplitude positive
and negative square wave increments with respect
40 to its A.-C. axis.
13. A wave modifying circuit for a source of
from its alternating-current axis by the instan
complex signals comprising means for limiting
taneous amplitude of said distorting signal as
positive and negative increments of said signals,
measured from its alternating-current axis to
means for amplifying said limited signal incre
produce a product signal.
45 ments, means for peak detecting said ampli?ed
8. In a system for secret transmission of a com
signals, means responsive to said detecting means
munication signal comprising frequency compo
for deriving control potentials, and means for ap
nents that lie within a certain frequency band,
plying said control potentials as variable bias po
a communication unit that includes means for
tentials to said limiting means to obtain there
producing a square wave distorting signal hav 50 from modi?ed signals having equal amplitude
ing A.-C. axial symmetry and comprising fre
positive and negative square wave increments
quency components that lie within a frequency
with respect to their A.-C. axis.
band at least a portion of which is common to a
14. In a secret telecommunication system for a
portion of said certain frequency band, and
communication signal, a coding wave generator
means for multiplying said communication sig 55 for producing a complex square coding wave hav_
nal by said distorting signal to produce a prod
ing equal positive and negative wave increments
uct signal, said multiplication being a multipli
with respect to its A.-C. axis, and means for mul~
cation of the signal values as measured from the
tiplying
the values of said communication signal
alternating-current axes of the signals.
9. A system for secret transmission of a com
munication signal from a transmitter to a re
ceiver, said transmitter including means for pro
ducing a square wave coding signal having A.-C.
axia1 symmetry and means for multiplying said
communication signal by said coding signal to
produce a product signal, means for transmit
ting said product signal to the receiver, said re
ceiver including means for producing a similar
square wave decoding signal having substantially
and said coding wave as measured from their
A.-C. axes to provide successive polarity reversals
of said communication signal for coding said sig
nal.
15. In a system of the type described in claim
14, means for generating a second substantially
65 identical coding wave, and means for multiplying
the values of said coded signal by said second cod
ing wave as measured from their A.-C. axes to
decode said communication signal.
16. The method of modifying a complex elec
the same waveform as said coding signal, and 70 trical wave to provide a substantially square wave
means for multiplying said product signal by said
having uniform peak values symmetrical with re
decoding signal, both of said multiplications being
spect to its A.-C. axis, comprising limiting said
complex wave at predetermined amplitude values,
from the alternating-current axes of the sig
amplifying
said limited wave, detecting said am
nals.
75 pli?ed wave potentials with respect to a reference
a multiplication of the signal values as measured
2,406,978
15'
potential, and controlling said limiting amplitude
16
‘peaks of substantially equal amplitude with re~
tudes.
17. A circuit for modifying a complex electrical
spect to the A.-C. axis of said square wave, said
circuit including limiting means for limiting the
positive amplitude and the negative amplitudes
plitude peak values symmetrical with respect to
to provide substantially equal amplitude positive
values in response to said detected wave ampli
of said complex wave at levels controlled by a bias
wave to provide a substantially square waveform
voltage applied to said limiting means, peak de
having uniform peak values symmetrical with re
tecting means responsive to the relative ampli
spect to its A.—C. axis, comprising means for lim
tudes of said positive and said negative peaks of
iting said complex Wave to provide waves having
said square Wave for generating a variable D.-C.
substantially square waveform and means respon
sive to said limited wave amplitudes with respect 10 voltage, and means for applying said, variable
D.-C. voltage as a- bias voltage to said limiting
to a point of reference potential,for biasing said
means whereby said limiting levels are controlled
limiter to provide square waves of uniform am
and negative peaks of said square wave.
their A.-C. axis.
18. A circuit for modifying a complex electrical 15
KARL R. WENDT.
wave to provide a wave having a substantially
ALDA
BEDFORD.
square waveform comprising positive and negative